The present invention relates to a combustion safety apparatus used chiefly for gas appliances.
As for an apparatus of this kind, there has been hitherto proposed in the prior art a type as that shown in FIGS. 1 to 3, for instance, having a combustion detecting element b such as an oxygen concentration cell element or the like which is provided in front of a main burner a, and the element b is so arranged that one electrode thereof is always so heated by a flame of a standing burner c as to be brought in a lack of oxygen condition, while the other electrode thereof is heated by the main burner a, so that when the main burner a is in its complete combustion condition, a flame d thereof is apart from the element b as shown by a solid line in FIG. 2 and thereby a difference in oxygen concentration is formed between the two electrodes and thereby a comparatively large output at the element b is generated, and, on the other hand, when the main burner a is in incomplete combustion condition, the flame d is so elongated as to reach the element b as shown by dotted lines in the same Figure and thereby the difference in oxygen concentration therebetween is decreased and the output is lowered. In addition, there is provided a safety device e such as a gas safety valve or the like, and the same is arranged to be controlled in operation directly or indirectly by the foregoing output of the element b.
It has been usual with this type of prior art apparatus, that the element b is formed into a long rectangular plate and is disposed to extend substantially in the same direction with the flame f of the standing burner c as illustrated. With this arrangement, however, there is involved disadvantages whereby--in the case where the element b is heated by the flame f which acts on the forward end portion of the element b as shown in FIG. 4, the flame f tends to go more or less off or beyond the forward end of the element b toward the front surface of the main burner a, and consequently the main burner a is partially influenced thereby and a back-fire is brought about at that portion. Furthermore, when the main burner a is brought in its incomplete combustion condition and consequently the flame d is elongated, the flame d is pushed back to retreat from the element b, by the flame f of the standing burner c, and thereby the detecting operation of the element b is spoiled.
Accordingly, such a preventive measure can be considered that the flame f of the burner c is so previously set as not to go beyond the forward end of the element b as shown in FIG. 6. In this measure, however, the heated area of the element b by the flame f becomes comparatively large and consequently the difference in oxygen concentration, that is, the output of the element b is increased that there is caused such an inconvenience that the difference cannot be sufficiently negated by the flame developed in the incomplete combustion condition.